As is well known, an optical signal generated from a light source, such as a laser, a laser diode or a light emitting diode, in an optical communication system is transmitted through an optical fiber. Optical connectors for connecting and switching two strands of optical fibers have been developed in a variety of configurations and should be manufactured so as to be able to accurately align the optical fibers so that the loss of the optical signal can be minimized. A ferrule of the optical connector is manufactured as an ultra-precision part with a tolerance of 1 μm or below. As for the ferrule of the optical connector, a cylindrical configuration is generally used with specifications as follows: 7 to 14 mm in length, 2.5 mm in outside diameter, and 125 to 127 μm in inside diameter of a hole for accommodating each optical fiber.
In order to guarantee precision and reliability of such a ferrule of an optical connector, a variety of items such as an inside diameter, an outside diameter and eccentricity are inspected. For example, a measuring apparatus disclosed in Korean Patent No. 269263 comprises a movable stage that can move along three axes, i.e. X axis, Y axis and Z axis, to measure straightness of an inside diameter of a ferrule, an illumination device for illuminating the ferrule with back light, a camera for photographing an inside diameter image of the ferrule projected by the illumination of the illumination device, and a computer for processing image data from the camera by means of a computer program. According to this technique, the inside diameter image is projected by the illumination of the illumination device passing through the interior of the ferrule defined by the inside diameter, the projected inside diameter image is photographed by the camera, and straightness of the inside diameter is measured by processing the inside diameter image data input from the camera by means of the computer program.
On the other hand, a measuring device disclosed in Korean Patent No. 198817 comprises a camera installed to be movable along three axes, i.e. X axis, Y axis and Z axis, so as to measure eccentricity of a ferrule, an illumination device for illuminating the interior of the ferrule defined by an inside diameter thereof with front light coaxially with an optical axis of the camera, and a computer for processing image data from the camera by means of a computer program. According to this technique, a test sample marked with a Cartesian coordinate system is photographed by the camera, an inside diameter image is projected by illuminating the inside diameter of the ferrule by the illumination device coaxially with the optical axis of the camera, and the projected inside diameter image is photographed by the camera. Then, Cartesian coordinate data of the test sample and the inside diameter image data that are input from the camera are processed by means of the computer program and thus eccentricity of the inside diameter with respect to the Cartesian coordinate data is measured.
However, the conventional techniques described above have a problem in that they are not appropriate to the inspection of the entire ferrule since they are constructed to perform only a separate inspection of the inside diameter of the ferrule. In particular, there is a problem in that since the outside diameter of the ferrule should be inspected using an additional device for measuring the outside diameter, the inspection process of the ferrule is substantially complicated and troublesome and thus a lot of time and manpower are required, which results in inefficiency of the inspection process. Further, although a total inspection that can completely guarantee the precision and reliability of the entire number of ferrules has been required, there is a substantial difficulty in performing the total inspection of the ferrules since the inspection can be made for only one ferrule at a time.